綁定XAML對SelectedItemChanged的ObservableCollection返回null

我建立一個文件瀏覽器，我有一個綁定到一個ObservableCollection我在想什麼，當有人點擊該文件夾（樹形視圖左側）上一個ListView它填充列表視圖並在文本塊中填寫正確的文件信息。綁定XAML對SelectedItemChanged的ObservableCollection返回null

我發現this幫助我到達我的所在地。但我仍然在文本塊中返回空值。感謝您的幫助！

我有一個private string start_Path

代碼來填充ListView控件：

private void load_ListView(string path) 
{ 
    var lv = File_List; 
    lv.Items.Clear(); 
    var search_Directory = new DirectoryInfo(path); 
    var item = new ListViewItem(); 
    try 
    { 

     foreach (var file in search_Directory.GetFiles()) 
     { 

      lv.Items.Add(file); 
     } 
    } 
    catch (Exception ex) 
    { 

    } 

} 
private void frm_File_Directory_Loaded(object sender, RoutedEventArgs e) 
{ 
    ListDirectory(foldersItem, start_Path.ToString()); 
} 

private void foldersItem_SelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e) 
{ 
    load_ListView(start_Path + "\\" + ((TreeViewItem)e.NewValue).Header.ToString()); 
    folder_Name = ((TreeViewItem)e.NewValue).Header.ToString(); 
    this.DataContext = File_Info_data.get_Files(start_Path + "\\" + ((TreeViewItem)e.NewValue).Header.ToString());    
}

的ObservableCollection：

public static ObservableCollection<File_Information> get_Files(string path) 
    { 
     var temp = new ObservableCollection<File_Information>(); 
     File_Information file; 
     FileInfo fileInfo = new FileInfo(path); 
     try 
     { 
      file = new File_Information 
      { 
       file_Size = fileInfo.Length, 
       date_Modified = fileInfo.LastWriteTime, 
       file_Type = get_File_Type(fileInfo.Extension) 
      }; 

      temp.Add(file); 

      return temp; 
     } 
     catch (Exception ex) { } 
     return null; 
    } 


    public static string get_File_Type(string extension) 
    { 
     string ext_Name = null; 
     switch (extension) 
     { 
      case @"xlsx": 
      case "xlsm": 
      case "xls": 
       ext_Name = "Excel File"; 
       break;   
      case "docx": 
      case "docm": 
      case "doc": 
       ext_Name = "Word Document"; 
       break; 
      case "pdf": 
       ext_Name = "PDF Document"; 
       break; 
      case "cad": 
       ext_Name = "CAD File"; 
       break; 
      case "DWG": 
       ext_Name = "AutoCAD Drawing"; 
       break; 
      case "jpg": 
       ext_Name = "JPEG image"; 
       break; 
      default: 
       ext_Name = "Unknown File Type"; 
       break; 
     } 
     return ext_Name; 
    }

XAML：

<ListView.ItemTemplate> 
     <DataTemplate> 

      <StackPanel Orientation="Horizontal"> 
       <Image Source="{Binding Converter={StaticResource PathConverter}}" 
           Height="20" 
           Width="20" 
           Stretch="UniformToFill" 
           /> 
       <TextBlock x:Name="file_Name" Text="{Binding}" Width="300"></TextBlock> 
       <TextBlock x:Name="Date_Modified" Text="{Binding date_Modified}" Width="200"></TextBlock> 
       <TextBlock x:Name="File_Type" Text="{Binding file_Type}" Width="150"></TextBlock> 
       <TextBlock x:Name="File_Size" Text="{Binding file_Size}" Width="150"></TextBlock> 
      </StackPanel> 

     </DataTemplate> 
    </ListView.ItemTemplate> 


</ListView>

來源

2015-08-03 user3120232

什麼，在哪裏回報'null'？ – Sinatr

View-model中的收藏屬性在哪裏？ –

我的文件名顯示出來，剩下的就是空 – user3120232

您可以改爲綁定喲ur SelectedItem改爲ViewModel中的某個房產。

<ListView ItemsSource="{Binding SomeCollection}" 
      SelectedItem="{Binding SelectedThing}" 
      ...

而且你的視圖模型將是這個樣子：

private Thing _SelectedThing; 

public Thing SelectedThing 
{ 
    get { return _SelectedThing; } 
    set 
    { 
     _SelectedThing = value; 

     //Call a method and send whatever has been selected. 
     DoSomethingUseful(value); 

     //TODO: Notify property changed 
    } 
}

然後，您可以實現方法：

private void DoSomethingUseful(Thing thing) 
{ 
    if (thing == null) 
     return; 

    //TODO: Whatever you need to do here. 
}

利用這一點，DoSomethingUseful方法都會被調用一次選擇變化。

來源

2015-08-03 13:12:33

這是更MVVM的做法，但它不會改變任何事情只能使對'強調null'檢查，這使得它（'null'檢查）可能的答案。 – Sinatr

如果@MikeEason的想法是正確的，那麼一個簡單的空檢查將做到：

private void foldersItem_SelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e) 
{ 
    if(e.NewValue == null) 
     return; 
    ... // rest of your code 
}

來源

2015-08-03 13:20:23 Sinatr

綁定XAML對SelectedItemChanged的ObservableCollection返回null

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